1. Field of the Invention
The present invention relates to a laser processing apparatus for applying a laser beam to the front side of a workpiece such as a wafer to thereby perform ablation.
2. Description of the Related Art
A plurality of semiconductor devices such as ICs (Integrated Circuits) and LSIs (Large Scale Integrated Circuits) are formed on the front side of a semiconductor wafer or a plurality of optical devices such as LEDs (Light Emitting Diodes) are formed on the front side of an optical device wafer. Such a wafer including the semiconductor wafer and the optical device wafer has a plurality of crossing division lines (streets) for partitioning the devices. A laser beam is applied to the front side of the wafer along the division lines by using a laser processing apparatus to thereby form a plurality of laser processed grooves on the front side of the wafer along the division lines. An external force is applied to the wafer thus having the laser processed grooves along the division lines, thereby dividing the wafer into the individual devices. These individual devices are installed in various electronic equipment such as PCs (Personal Computers) and LED lights, thus manufacturing the electronic equipment having the devices.
It is known that when a laser beam having an absorption wavelength to the wafer is applied to the wafer in this laser processing step, fine dust particles called debris are generated and scattered to stick to the front side of each device, causing a deterioration in device quality. To cope with this problem, there has been proposed a processing method including the steps of forming a protective film on the wafer before laser processing and cleaning off the protective film and the debris deposited on the protective film after laser processing. There has also been proposed a laser processing apparatus including a nozzle for blowing air along the optical axis of a focusing objective lens and collecting means for sucking the debris from the periphery of the nozzle (see Japanese Patent Laid-open Nos. 2007-69249 and 2011-189400, for example).